Definitions for "Ultrafast"
In physics, the adjective ultrafast describes events that occur on femtosecond (10-15 s) to picosecond (10-12 s) timescales. Once impossible to observe, ultrafast phenomena are now extensively studied thanks to advances in the design of pulsed dye lasers and more recently with the invention of the pulsed Ti:sapphire laser, which can create pulses as short as 5 femtoseconds (roughly two optical cycles) when mode-locked.